Control system for a load handling apparatus

ABSTRACT

A control system ( 40 ) for a machine ( 10 ) which includes a load handling apparatus ( 14 ), the load (L) being moveable relative to a body ( 12 ) of the machine by the load handling apparatus ( 14 ), the machine ( 10 ) including a pivot (C) about which a tipping moment is produced by the load (L), the load handling apparatus (L) including an actuator ( 24 ) and being capable of moving the load (L) to a position at which the tipping moment is at a predetermined threshold value, the control system ( 40 ) including a sensor ( 30 ) to sense the tipping moment and in use, to provide an input to a controller ( 32 ), the controller ( 32 ) being responsive to the input to influence operation of the actuator ( 24 ) so that in the event that the sensor ( 30 ) senses that the value of the tipping moment is approaching the threshold value, the speed of movement of the load (L) is progressively reduced.

This invention relates to a control system for a machine of the kindwhich includes a load handling apparatus, the load being moveablerelative to a body of the machine by the load handling apparatus.

One example of such a machine is a wheeled load handling machine whichhas a body, a ground engaging structure including a pair of axles eachcarrying wheels, and the machine including a load handling apparatuswhich includes a lifting arm. The lifting arm is moveable by one or moreactuators to move the load, the load producing a tipping moment abouteither an axis of rotation of one of the pairs of wheels, or aboutanother pivot where for example, stabilisers are used to stabilise thebody relative to the ground during load handling operations.

In each case, the lifting arm may move the load to a position at whichthe tipping moment is at a threshold value at which the machine maybecome unstable.

Thus it is known to sense the tipping moment, for example by sensing adecreasing load on the pair of wheels remote from the pivot, as thetipping moment reaches the threshold critical value, to operate a safetydevice which stops further operation of the actuator or actuators.

Such an arrangement may operate satisfactorily for some lifting arm/loadmovements, but unless the threshold value is set with a significantsafety margin, for some load movements an abrupt cessation of movementcan result in machine instability due to the inertia of the load, and ofthe lifting arm, The problem is particularly pronounced as the liftingarm is lowered after having been loaded at long reach and at height, aslowering of the lifting arm, increases the tipping moment and an abruptcessation of movement can result in the machine tipping forwards.

It is known to provide a machine operator with a visual indication ofthe value of the tipping moment, and therefore a skilled and attentiveoperator may be able to determine when the tipping moment is approachingthe threshold value and the operator may thus take action such asretracting the load, where the lifting arm is capable of such operation,to avoid machine instability. However this relies on operator skill andattentiveness, and moreover such reliance would be inappropriate wherethe machine does not have an operator, e.g. is robot or remotecontrolled.

According to a first aspect of the invention we provide a control systemfor a machine which includes a load handling apparatus, the load beingmoveable relative to a body of the machine by the load handlingapparatus, the machine including a pivot about which a tipping moment isproduced by the load, the load handling apparatus including an actuatorand being capable of moving the load to a position at which the tippingmoment is at a predetermined threshold value, the control systemincluding a sensor to sense the tipping moment and in use, to provide aninput to a controller, the controller being responsive to the input toinfluence operation of the actuator so that in the event that the sensorsenses that the value of the tipping moment is approaching the thresholdvalue, the speed of movement of the load is progressively reduced.

Thus utilising the present invention, stability of the machine duringload movements which may otherwise cause instability, is automaticallymaintained and does not rely on operator skill.

In a preferred embodiment, the load handling apparatus is a lifting armwhich is moveable about a generally horizontal axis relative to the bodyof the machine, the arm thus being capable of raising and lowering theload upon operation or a first actuator, the controller influencingoperation of the first actuator as the tipping moment approaches thethreshold value. The lifting arm may include a plurality of relativelymoveable sections, which may for example be telescopic, and thecontroller may alternatively or additionally influence operation of asecond actuator which relatively moves the arm sections as the tippingmoment approaches the threshold value. Further, the arm may carry a loadhandling implement, such as lifting forks, which are movable on the armby operation of a third actuator and the controller may additionally oralternatively influence operation of the third actuator as the tippingmoment approaches the threshold value.

In each case, the speed of movement of the load is progressively reducedand desirably is stopped altogether when the tipping moment is at thethreshold value, which preferably is set so that instability of themachine is avoided.

The machine may include a ground engaging structure by which the machineis supported on the ground. The structure may include a pair ofsupports, the tipping moment being produced about a pivot axisestablished by one of the supports. The tipping moment may be sensed bythe sensor sensing loading of one of the supports.

In one example the machine is a so called wheeled load handling machinehaving a ground engaging structure including a pair of supports providedby axles which each carry wheels. Thus the tipping moment may beproduced about a rotational axis of one of the pairs of wheels whilstthe sensor may sense the loading on the other pair of wheels.

As the value of the tipping moment approaches the threshold value, theloading on the other pair of wheels will reduce which reduction inloading will be sensed by the sensor.

The actuator the operation of which is influenced, may be a fluidoperated actuator such as a double acting linear hydraulic ram. Thecontroller may influence operation of the actuator by reducing a flow offluid to or from the actuator, regardless of any control input e.g. froma machine operator, so that the controller responds to the input fromthe sensor sensing the tipping moment by overriding any such controlsignal.

Thus the system may include a main control valve for providing fluid tothe actuator under operator or robot/remote control, and a valve whichis independent of the control valve, but responsive to the controller toreduce the flow of fluid to or from the actuator as the sensed tippingmoment approaches the threshold value.

The sensor may be a transducer which provides an electrical input signalto the controller, whilst a control signal to influence actuatoroperation may be an electrical or fluid signal.

Where the load handling apparatus includes a plurality of actuators, forexample where the load handing apparatus is a raisable and lowerablelifting arm which may be telescopic and/or may include a load handlingimplement mounted on the arm, each operated by respective fluid operatedactuators, the controller may influence the operation of one of theactuators as the value of the tipping moment approaches the thresholdvalue, for example by reducing the permitted flow of fluid from theactuator, and may prevent the flow of fluid to or from the remainingactuator or at least one of the remaining actuators if the tippingmoment value reaches the threshold value, whilst permitting only furtheractuator correctional operation which will result in a reduction in thetipping moment.

However, for example where the load handling implement is a liftingforks, during any permitted correctional actuator operation, theattitude of the lifting forks relative to the ground may be maintained.

For example the machine may include a displacement actuator which isoperated as the lifting arm is raised and lowered to exchange fluid withthe third actuator which controls the attitude of the load handlingimplement relative to the ground, and during correctional actuatoroperation, when the third actuator may be isolated, fluid pressure in acircuit containing the third and displacement actuators may bemaintained.

The controller may operate according to an algorithm which enables thecontroller to ignore transient changes of loading sensed by the sensoras a result of changing machine dynamics or of reaction to initial liftarm movements.

According to a second aspect of the invention we provide a machinehaving a control system according to the first aspect of the invention.

According to a third aspect of the invention we provide a load handlingapparatus controlled by a control system according to the first aspectof the invention.

According to a fourth aspect of the invention we provide a method ofoperating a load handling system according to the third aspect of theinvention including progressively reducing to speed of lowering of theload in response to increasing machine instability.

Embodiments of the invention will now be described with the aid of theaccompanying drawings in which:—

FIG. 1 is a side illustrative view of a machine embodying the invention;

FIG. 2 is a rear view of the machine shown in FIG. 1;

FIG. 3 is an illustrative hydraulic circuit diagram of the machine ofFIGS. 1 and 2, which incorporates features of the control system of theinvention.

Referring to the drawings a load handling machine 10 includes a body 11which includes in this example an operator's cab 12, at one sidelongitudinally of the body 12, and a mounting 13 for a lifting arm 14 atan opposite side of the body 12, the mounting 13 being provided in thisexample towards a rear of the body 12, such that the lifting arm 14extends forwardly from a pivot axis B alongside the cab 12.

The body 12 is supported on and may be driven over the ground on aground engaging structure which includes a pair of front wheels 16carried on a front axle which usually is fixed relative to the body 12,but may be suspended therefrom as desired, and a rear pair of wheels 17also carried on an axle 19, the rear axle 19 being in this example,coupled to the body 12 by a pivot 20 which permits oscillating rear axle19 movement about a pivot axis A, relative to the body 12.

The lifting arm 14 in this example includes two relatively telescopicsections 22, 23, an inner of the sections 22 being mounted by themounting 13, and the outer 23 of the sections carrying a load handlingimplement 26 which in this example is a pair of lifting forks. Inanother example the arm 14 may include more than two telescopic orotherwise relatively extendible sections, or a single section only.

The arm 14 is raisable and lowerable by operation of a lifting actuator24, which is a double acting hydraulic linear actuator. The outersection 23 of the arm 14 may be extended/retracted relative to the innersection 22 by a further double acting hydraulic linear extensionactuator 25 which is shown mounted exteriorly of the arm 14 althoughpractically may be mounted interiorly of the arm 14. The load handlingimplement 26 is moveable about the pivot axis D by a yet further doubleacting linear hydraulic fork actuator 27.

The actuators 24, 25 and 26 are all controlled in this example by anoperator in cab 12 operating controls to operate a main control valve44, which is indicated in FIG. 3, but in another example the actuatorsmay be remotely controlled by a computer i.e. may be robot controlled.

It will be appreciated that a load L carried by the arm 14 will producea tipping moment about a pivot axis C. In this example of a wheeled loadhandling machine 10 with the lifting arm 14 being rearwardly mounted andextending forwardly, the pivot C will be coincident with the axis ofrotation of the front wheels 16. However, where for example stabilisers32 are provided which can be lowered into contact with the ground duringsome load handling operations, perhaps to raise the front wheels 16 offthe ground, the pivot axis may otherwise be located.

Even though the weight of the load L is counterbalanced by the mass ofthe machine 10 and in particular in this example by the machine engine Ewhich may be positioned at the rear of the body 12 as indicated, orelsewhere, if the load L is moved forwardly of the tipping axis C beyonda certain position, dependant upon the magnitude of the load, it will beappreciated that the stability of the machine 10 will decrease as themachine 10 will tend to tip about the tipping axis C. Such load Lmovement may occur for example as the lifting arm 14 is extended, or asis pertinent to the present invention, upon lowering of a load L from ahigh position, e.g. as indicated in dotted lines to a lowered positionshown in dotted lines.

The resultant increase in the tipping moment about tipping axis C isconventionally determined by sensing a reduction in loading on the rearaxle 19 on which the body 12 is supported.

Thus a tipping moment sensor 30 is provided, such as a load cell orother transducer to sense the loading on the axle 19, in this example atthe pivot 20 connection of the rear axle 19 to the body 12. The sensor30 is operative to provide an input to a controller 32 indicative ofrear axle 19 loading and thus of the tipping moment about the tippingaxis C.

In known arrangements, when the input to the controller 32 indicatesthat the tipping moment is about to increase to such an extent that themachine 10 is about to tip forwardly about the tipping axis C, thecontroller 32 acts to prevent further forward movement of the load Lrelative to the body 12. For example the extension actuator 25 may beprevented from extending further and/or the lifting actuator 24 may beprevented from further lowering the lifting arm 14.

In the latter case, because the inertia of a loaded lifting arm and loadL may be massive, an abrupt cessation of the downward movement of thearm 14 can result in the machine 10 tipping about the tipping axis Cunless the threshold value of the tipping moment permitted is set to animpracticably acceptable safety limit.

Referring particularly to FIG. 3, a control system 40 is shown partiallyintegrated within a hydraulic system for operating and controlling theactuators 24, 25, 27.

When the control system 40 is actuated, for example in anticipation ofhandling a heavy load, a solenoid valve 41 is closed e.g. by a machine10 operator operating a switch in the cab 12, so that fluid to a rodside 24 a of the lifting actuator 24 from main control valve 44 as thelifting arm 14 is lowered, is constrained to flow through a proportionalvalve 42, via a restrictor 43. The restrictor 43 reduces permitted flowfrom that which would be permitted when the control system 40 is notactive. Thus the lowering speed of the lifting arm 14 will beconstrained in any event.

However the flow of fluid to the rod side 24 a of the lifting actuator24 may be further restricted by the proportional valve 42 as hereinafterexplained, to maintain the value of the tipping moment of the machineabout axis C below a threshold value.

In parallel with the proportional valve 42 there is a counterbalancevalve 45 which permits fluid from the main control valve 44 to bedirected to the rod side 24 a of the actuator 24 when it is desired tolower the lifting arm 14 when the control system of the invention isinactive.

In the event that from the input from the sensor 30, the controller 32determines that the value of the tipping moment about pivot C isapproaching a predetermined threshold value, for example is about 65% ofthe permitted tipping moment threshold value, the controller 32 acts toprevent the value of the tipping moment exceeding the threshold value.

If the lifting arm 14 is being lowered, the controller 32 signals theproportional valve 42 to reduce the permitted flow of fluid to the rodside 24 a of the actuator 24 progressively as the lifting arm 14 iscontinued to be lowered, until further lowering of the lifting arm 14 isprevented altogether when the value of the tipping moment reaches thethreshold value, as all fluid flow to the rod side 24 a of the actuator24 is prevented by the proportional valve 42 closing completely orsubstantially completely.

It can be seen that the proportional valve 42 is in this examplesolenoid operated, so that the controller 32 provides an electricalcommand signal to the proportional valve 42 although in another examplea fluid pressure signal may be provided by the controller 32.

The machine operator in the cab 12 may reverse operation of the liftingactuator 24 by operating the main valve 44 to direct fluid to a cylinderside 24 b of the actuator 24 to raise the lifting arm 14 and thus reducethe tipping moment about axis C, and/or may retract the extensionactuator 25 to move the load L closer to the tipping axis C, byoperating the main control valve 44 to direct fluid to a rod side 25 aof the extension actuator 25.

Upon the threshold tipping value being reached, when further lowering ofthe lifting arm 14 will be prevented, the controller 32 also acts toopen a further solenoid operated valve 48 in the circuit to prevent anyoperation of the extension actuator 25 which would move the load Lfurther away from the tipping axis, and to isolate altogether theactuator 27 which is otherwise operative to move the lifting forks 26.

This is achieved as the further solenoid operated valve 48 when openedprovides a by-pass to tank T. Thus in the event that the main controlvalve 44 is operated such as would otherwise extend the lifting arm 14,fluid in line 50 which would otherwise pass to cylinder side 25 b of theextension actuator 25 to extend the extension actuator 25, will berelieved to tank T, via a non return valve 51 and the valve 48, via line52.

Moreover in the event that the operator operates the main valve 44 suchas otherwise to operate the actuator 27 to move the lifting forks 26about axis D on the arm 14, again fluid in either of lines 55, 56 whichwould otherwise act to operate the actuator 27, will be relieved to tankT, via one or other of the non-return valves indicated at 59, 60 and thevalve 48, via line 52.

If desired, where the machine 10 has stabilisers S which may be loweredinto engagement with the ground during some working operations, a reliefvalve as indicated at 62 may be provided which restricts the angle towhich the lifting arm 14 may be raised when the stabilisers S are notlowered. For example, when the machine 10 is performing workingoperations with the stabilisers S raised, such that there is greaterpotential for machine 10 instability, when the arm 14 is raised at anangle of 45°, the relief valve 62 may be opened e.g. by operation of thecontroller 32, so that further fluid directed from the main controlvalve 44 to the rod side 24 a of the lifting actuator 24 is relieved totank T.

Referring again to FIG. 1 it can be seen that the machine 10 includes adisplacement actuator 64 between the lifting arm 14 and the body 12 ofthe machine. The displacement actuator 64 is a double acting hydraulicactuator, a piston 64 a of the actuator 64 being extended relative to acylinder 64 b thereof, as the lifting arm 14 is raised, and beingretracted into the cylinder 64 b as the arm 14 is lowered.

As indicated in FIG. 3, in normal operation, the displacement actuator64 is provided in parallel to the actuator 27 which moves the liftingforks 26 about the axis D, and so as the arm 14 is raised and lowered,the attitude of the forks 26 or other load handling device 26 relativeto the ground, may be maintained without intervention of the operatoroperating the main control valve 44 to operate the forks actuator 27.

Such an arrangement is known, but it will be appreciated that in theevent that, with the control system of the invention, the relief valve48 is opened to relieve fluid in that part of the circuit containing thefork actuator 27, such automatic attitude maintenance will be lost. Soin the event that the operator operates the lifting actuator 24 tocorrect machine 10 imbalance by raising the lift arm 14, until therelief valve 48 again is closed by the controller 32, the attitude ofthe forks 26 relative to the ground will not be maintained.

However, to accommodate this, there is provided in each of the fluidlines 55 and 56 from the fork actuator 27 and displacement actuator 64,a counterbalance valve 70, 71 respectively, which closes automaticallyupon loss of pressure in the lines 55, 56 as the relief valve 48 isopened, whilst permitting the transfer of fluid between the forkactuator 27 and the displacement ram 64 trapped in that part of thefluid circuit upstream of the counterbalance valves 70, 71.

Other features of the control circuit 40 are as follows.

In the lines 55, 56 to and from the fork actuator 27 and displacementactuator 64, there are provided solenoid operated restrictor valves 80,81 which when operated e.g. by the controller 32 when the control systemis actuated, may restrict operational speed of the fork actuator 27, byrestricting fluid flow to and from the actuators 27, 64 in proportion tothe degree of instability of the machine 10 as sensed by the load sensor30.

Other check valves and the like, e.g. as indicated at 85, 86 and 87 maybe provided to ensure proper operation of the circuit.

It has been found that in some conditions, when commencing lowering ofthe load L e.g. from a high position, there is an initial reaction whichis transmitted through the machine 10 to the load sensor 30 whichindicates a sudden increase in loading on the rear axle 19. To preventthe control system reacting to such transient conditions, preferably thecontroller 32 is adapted to operate according to an algorithm whichignores such transient conditions. For example upon initiating loweringof the lifting arm 14, the controller 32 may be arranged not to respondto the sensor 30 input for say, one or two seconds, by which time steadystate conditions will ensue.

Also, it will be appreciated that a false indication may be receivedfrom the sensor 30 of impending machine 10 instability as a result ofchanging machine 10 dynamics during some load handling operations, forexample during loading/unloading of the lifting forks 26. The controller32 may be programmed to recognise such irregular indications, forexample by responding only to a smoothly progressively changing tippingmoment, rather than sudden changes in loading.

Preferably, the controller 32 provides a visual indication on anindicator 33 in the operator's cab 12 to the operator of the stabilityof the machine 10 so that a skilled operator may still exercise hisskill in avoiding unstable conditions with reference to the indicator33. For example such an indicator may include an array of lights, e.g.LED lights, the array being increasingly lit up as instability of themachine 10 increases.

Various other modifications may be made without departing from the scopeof the invention as will be apparent to the person skilled in the art.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaning the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilised forrealising the invention in diverse forms thereof.

1. A control system for a machine which includes a load handlingapparatus, the load being moveable relative to a body of the machine bythe load handling apparatus, the load handling apparatus being a liftingarm which is moveable about a generally horizontal axis relative to thebody of the machine, the arm thus being capable of raising and loweringthe load upon operation of a fluid operated actuator the machineincluding a pivot about which a tipping moment is produced by the load,the load handling apparatus being capable of lowering the load to aposition at which the tipping moment is at a predetermined thresholdvalue, the control system including a sensor to sense when the value ofthe tipping moment is approaching the threshold value and, to provide aninput to a controller in response, the controller being responsive tothe input to operate a proportional valve to reduce the flow of fluid tothe actuator so that the speed of movement of the load is progressivelyreduced as the lifting arm is continued to be lowered.
 2. (canceled) 3.(canceled)
 4. A system according to claim 1 wherein the lifting armincludes a plurality of relatively moveable sections, and the controllerinfluences operation of a second actuator which relatively moves the armsections as the tipping moment approaches the threshold value.
 5. Asystem according to claim 4 wherein the relatively moveable sections aretelescopic.
 6. A system according to claim 1 wherein the arm carries aload handling implement which is movable on the arm by operation of athird actuator and the controller influences operation of the thirdactuator as the tipping moment approaches the threshold value.
 7. Asystem according to claim 6 wherein the load handling implement is aloading forks.
 8. A system according to claim 1 wherein the speed ofmovement of the load is progressively reduced and is stopped altogetherwhen the tipping moment is at the threshold value.
 9. A system accordingto claim 1 wherein the machine includes a ground engaging structure bywhich the machine is supported on the ground the ground engagingstructure including a pair of supports, the tipping moment beingproduced about a pivot axis established by one of the supports, thetipping moment being sensed by the sensor sensing loading of one of thesupports.
 10. (canceled)
 11. (canceled)
 12. A system according to claim9 wherein the machine is a wheeled load handling machine having a groundengaging structure including a pair of supports provided by axles whicheach carry wheels.
 13. A system according to claim 12 wherein thetipping moment is produced about a rotational axis of one of the pairsof wheels and the sensor senses the loading on the other pair of wheels.14. (canceled)
 15. (canceled)
 16. A system according to claim 1 whereinthe fluid operated actuator is a double acting linear hydraulic ram. 17.A system according to claim 1 wherein the sensor is a transducer whichprovides an electrical input signal to the controller.
 18. A systemaccording to claim 8 wherein the load handling apparatus includes aplurality of actuators, and in the event that the controller preventsthe flow of fluid to or from the raising and lowering actuator if thetipping moment value reaches the threshold value, the controller permitsone or more of the further actuators to be operated to perform acorrectional operation which will result in a reduction in the tippingmoment.
 19. A system according to claim 18 wherein where the loadhandling implement is a lifting forks, and during any permittedcorrectional actuator operation, the attitude of the lifting forksrelative to the ground is automatically maintained.
 20. A systemaccording to claim 19 wherein the machine includes a displacementactuator which is operated as the lifting arm is raised and lowered toexchange fluid with an actuator which controls the attitude of the loadhandling implement relative to the ground, and during correctionalactuator operation, when the raising and lowering actuator is isolated,fluid pressure in a circuit containing the attitude controlling anddisplacement actuators is maintained.
 21. A system according to claim 1wherein the controller operates according to an algorithm which enablesthe controller to ignore transient changes of loading sensed by thesensor as a result of changing machine dynamics or of reaction toinitial lift arm movements.
 22. (canceled)
 23. A machine having acontrol system which includes a load handling apparatus, the load beingmoveable relative to a body of the machine by the load handlingapparatus, the load handling apparatus being a lifting arm which ismoveable about a generally horizontal axis relative to the body of themachine, the arm thus being capable of raising and lowering the loadupon operation of a fluid operated actuator the machine including apivot about which a tipping moment is produced by the load, the loadhandling apparatus being capable of lowering the load to a position atwhich the tipping moment is at a predetermined threshold value, thecontrol system including a sensor to sense when the value of the tippingmoment is approaching the threshold value and, to provide an input to acontroller in response, the controller being responsive to the input tooperate a proportional valve to reduce the flow of fluid to the actuatorso that the speed of movement of the load is progressively reduced asthe lifting arm is continued to be lowered.
 24. (canceled)
 25. A loadhandling apparatus controlled by a control system which includes a loadhandling apparatus, the load being moveable relative to a body of themachine by the load handling apparatus, the load handling apparatusbeing a lifting arm which is moveable about a generally horizontal axisrelative to the body of the machine, the arm thus being capable ofraising and lowering the load upon operation of a fluid operatedactuator the machine including a pivot about which a tipping moment isproduced by the load, the load handling apparatus being capable oflowering the load to a position at which the tipping moment is at apredetermined threshold value, the control system including a sensor tosense when the value of the tipping moment is approaching the thresholdvalue and, to provide an input to a controller in response, thecontroller being responsive to the input to operate a proportional valveto reduce the flow of fluid to the actuator so that the speed ofmovement of the load is progressively reduced as the lifting arm iscontinued to be lowered.
 26. (canceled)
 27. (canceled)
 28. (canceled)